The invention is related to an apparatus for checking the tightness of a tank venting system that serves to vent a fuel tank of a motor vehicle whose internal combustion engine has an intake tube, or in other words checking the system for leaks.
It is known that checking for a leak in a tank venting system can be achieved by working with an overpressure or a vacuum; according to German Patent 40 03 751A1, these pressures depend on the operating requirements. It is further known that for leak checking the tank system, an overpressure can be produced with the help of an electrically actuated reciprocating piston or by means of a special air pump.
In the systems in which a vacuum or an overpressure occurs, depending upon the operating requirements of the engine having the tank to be checked, it is, at least as concerns the production of an overpressure, frequently not possible to easily bring about the proper operating requirements for producing an overpressure. On the other hand, in check systems working with a reciprocating piston or an air pump, an additional technical expenditure is required which results in higher cost and/or an increased susceptibility to failure of the entire system.